i4000462 in 23andMe reports, known as 1100delC, has been associated with a 1.4x to 4.7x increased risk for breast cancer. Carriers of one copy of this deletion produce half the normal amount of the CHEK2 protein. This deletion is one of the more common genetic variants associated with breast cancer.

"The aim of this study was to determine whether common polymorphic variants in CHEK2 are associated with an increase in breast cancer risk. We examined two variants: an insertion of a single nucleotide in intron 1 rs3841692 and a single nucleotide a to g substitution rs1805129, which is a silent alteration in codon 84 of the coding sequence." [1]